Although it will become evident to those skilled in the art that the present invention is applicable to a variety of implantable medical devices utilizing pulse generators to stimulate selected body tissue, the invention and its background will be described principally in the context of a specific example of such devices, namely, an ICD or implantable cardioverter-defibrillator for delivering electrical therapy to terminate ventricular tachycardia or ventricular fibrillation via an external connector assembly having lead-receiving receptacles. The appended claims are not intended to be limited, however, to any specific example or embodiment described herein.
ICDs and other implantable medical devices such as pacemakers are hermetically packaged to isolate the device from the body environment. Such devices require that electrical signals be passed between the packaged device and its external connectors, without compromising the hermeticity of the package. Depending on the configuration of the implantable device, there may be multiple electrical paths required between the device and its external connectors. These paths must be electrically and mechanically integrated with the device to provide a safe, long-term arrangement which does not compromise the hermetic package.
Typically, electrical coupling between the electronic circuits of the implantable device and the external connections provided by a connector assembly mounted outside of the implantable device are provided by a feedthrough assembly. The feedthrough assembly extends through the hermetically sealed outer wall of the device and into the connector assembly so as to couple the electronic circuits within the implantable device to lead-receiving receptacles within the connector assembly. Common feedthrough assemblies contain a number of wires equal to the number of electrical paths required for the configuration. The wires are placed in a ceramic sleeve and are sealed and mechanically secured to the sleeve, such as by brazing. The ceramic sleeve is secured to a weld ring, such as by brazing, following which the weld ring is integrated into the housing wall of the implantable device, such as by laser welding. The resulting feedthrough assembly has many individual seals and exposed lengths of wire.
Feedthrough assemblies of the type described have a number of potential problems. One such problem results from the large number of seals required. Because the plurality of wires and the weld ring each require a separate seal, the large number of seals increases the chances of a compromised seal and the resulting loss of hermeticity. Moreover, the exposed wires act as an antenna for environmental noise sources. Such noise compromises the quality of the signal transmitted, and this can lead to misinterpretation by the implantable device. Additionally, the wires can be damaged by misalignment or bending during handling of the feedthrough assembly.
Traditionally, single and dual chamber ICDs use a single feedthrough with the appropriate number of leads depending on the device's bore configuration.
Heart failure ICDs require eight leads due to the additional LV lead connector bore. This is accomplished by using two quad (four lead) filtered feedthrough assemblies. These parts consist of ceramic terminals, ceramic EMI capacitor, platinum-iridium wires and a titanium housing which encompasses the whole assembly. The titanium housing has a built-in flange for mounting and hermetically welding to the device.
The feedthrough wires are connected to the electronic assembly through solder joints to an output flex. The feedthroughs are located on the device case and laser welded in place during peripheral welding of the device.
The process of assembly and laser welding of two feedthroughs to the heart failure ICD devices have proven to be laborious and slow. Due to clearance needed between two feedthroughs to prevent reflection damage and weld interference, extra space is required for the device as well.
After peripheral welding, devices are backfilled with nitrogen. This is done through an opening called a backfill port which may be a separate titanium part welded onto the case. This requires a subassembly step with dedicated weld requirements and procedures. In addition careful positioning of the part is needed to make sure the port is not blocked off inside the device.
Typical disclosures of implantable medical devices having shielded and filtered feedthroughs can be found, for example, in U.S. Pat. Nos. 5,620,476 and 5,683,435 to Truex et al. comprising a feedthrough assembly in which plural wires are eliminated in favor of a single, monolithic structure of elongated configuration which extends through and is hermetically sealed to a sealing device such as a weld ring. The weld ring is, in turn, hermetically sealed within the housing wall of the implantable device. The monolithic structure comprises a multilayered structure in which an array of printed conductors provides the connections between the electronic circuits of the implantable device and the lead-receiving receptacles of the connector assembly. Electric field shielding of the printed conductors is provided by a conductive boot surrounding the printed conductors and being coupled to ground. The conductive boot may be provided by printed ground planes on opposite sides of the printed conductors within a multilayered structure. Filtering is provided by capacitors coupled between positive contacts and ground contacts within a second portion of the feedthrough assembly residing within the implantable device.
In another instance as presented in U.S. Pat. No. 6,349,025 to Fraley et al., a filtered feedthrough is disclosed that does not block passage of gas in a helium leak test and enables testing of the hermeticity of the feedthrough while inhibiting high voltage arcing in single filtered feedthrough and multiple filtered feedthrough array configurations. Still another instance is presented in U.S. Pat. No. 6,414,835 to Wolf et al. according to which a capacitive filtered feedthrough assembly is formed in a solid state manner to employ highly miniaturized conductive paths each filtered by a discoid capacitive filter embedded in a capacitive filter array. Yet another instance is presented in U.S. Pat. No. 6,660,116 to Wolf et al. which discloses a capacitive filtered feedthrough assembly formed in a solid state manner to employ highly miniaturized conductive paths each filtered by a discoid capacitive filter embedded in a capacitive filter array.
It was in light of the foregoing that the present invention was conceived and has now been reduced to practice.